Capillary electrophoresis (CE) is an analytical separation technique that employs a high voltage drop across a capillary column (e.g., of fused silica) which is about 5 to 100 microns (.mu.m) in inner diameter. CE offers high speed, good resolution and efficiency that are inherent in electrokinetic separation techniques. Since CE is a liquid phase system typically containing more than 90% of aqueous phase at neutral pH, another advantage of CE is that the structural conformation of the biomolecules can be maintained. The maintenance of structural conformation has further utility in the ease of changing the environment to cause structural alterations, which in turn can create a switching device such as in the case of a pH or organic solvent or a temperature change. CE lends itself to micromanipulations. Typical injection volumes in CE are 2 to 10 nanoliters (nL) and may contain analytes as little as 100 attomole to 1 femtomole. A general reference on capillary electrophoresis is the Handbook of Capillary Electrophoresis edited by James P. Landers (CRC Press, Ann Arbor, 1994).
Recently, much effort has been devoted to attaching biomolecules to the surface of a substrate. One application of such effort is in creating biomolecular arrays for detection of chemicals. For example, Fodor, et al., "Light-directed, Spatially Addressable Parallel Chemical Synthesis," Science, Vol. 251, 767-773 (1991) disclose high-density arrays formed by light-directed synthesis. Such arrays can be used for antibody recognition. Biomolecular arrays are also described by E. Southern (PCT Publication WO 89/10977) for analyzing polynucleotide sequences. Such biomolecular arrays lend themselves to a large number of applications, from DNA and protein sequencing to DNA fingerprinting and disease diagnosis. Techniques for synthesizing a polymer array on an optical substrate are described by Fodor et al. (1991) supra; PCT publications WO 91/07087, WO 92/10587, WO 92/10588; and U.S. Pat. No. 5,143,854. The techniques of attaching chemicals to substrates and to one another in the aforementioned documents are incorporated by reference herein.
Today, however, positioning a large number of different chemicals, such as biomolecules, on a substrate in distinct locations is a difficult task. Typically, present day processes involve synthesizing an array of different ligands onto a substrate using photolithographic techniques. Such technology has serious disadvantages for the microfabrication of a large number of very small features, such as biochemical arrays. The process of photolithography is expensive and not suitable for mass production. Current technology cannot produce features of sufficiently small size, e.g., 1 micron or less. What is needed is an effective technique for arranging at different locations on a substrate a large number of different chemicals that are to be affixed on the substrate.